The Industrial, Scientific, and Medical (ISM) bands between 2400 MHz and 2483.5 MHz is utilized by nearly all Wireless Local Area Networks (WLAN) and Wireless Personal Area Networks (WPAN) systems. Currently, the most significant of these are Bluetooth networks and networks that operate according to the IEEE 802.11 standards (However, IEEE 802.11a operates in the 5 GHz ISM band).
Bluetooth defines a short-range radio network, originally intended as a cable replacement. It can be used to create ad hoc networks of up to eight devices, where one device is referred to as a master device and the other devices are referred to as slave devices. The slave devices can communicate with the master device and with each other via the master device. Bluetooth devices are designed to find other Bluetooth devices within their communications range and to discover what services they offer. Bluetooth networks may utilize 79 channels, each having a 1 MHz bandwidth. To enhance robustness, Bluetooth networks perform frequency hopping among all or some of these 79 channels.
WLANs are local area networks that employ high-frequency radio waves rather than wires to exchange information between devices. IEEE 802.11 refers to a family of WLAN standards developed by the IEEE. In general, WLANs in the IEEE 802.11 family provide for 1 or 2 Mbps transmission in the 2.4 GHz band (except IEEE 802.11a) using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS) transmission techniques. Within the IEEE 802.11 family are the IEEE 802.11b and IEEE 802.11g standards.
IEEE 802.11b (also referred to as 802.11 High Rate or Wi-Fi) is an extension to IEEE 802.11 and provides for data rates of up to 11 Mbps in the 2.4 GHz band. This provides for wireless functionality that is comparable to Ethernet. IEEE 802.11b employs only DSSS transmission techniques. IEEE 802.11g provides for data rates of up to 54 Mbps in the 2.4 GHz band. For transmitting data at rates above 20 Mbps (or when all devices are IEEE 802.11g capable), IEEE 802.11g employs Orthogonal Frequency Division Multiplexing (OFDM) transmission techniques. However, for transmitting information at rates below 20 Mbps, IEEE 802.11g employs DSSS transmission techniques. The DSSS transmission techniques of IEEE 802.11b and IEEE 802.11g involve signals that are contained within a 22 MHz wide channel. These 22 MHz channels are within the ISM band.
Increasingly, bands such as the ISM band are being consumed by various types of communications devices that utilize the same spectral portions. This is becoming a problem because the spectrum usage of WLAN and WPAN systems are regulated in only a very coarse manner. Therefore, transmissions from such communications devices may interfere with each other. In addition, interfering energy in the ISM bands may be caused by other sources. Examples of such sources include microwave ovens and harmonics of cellular telephony transmissions (e.g., GSM and IS-95 transmissions).
In order for communications networks to operate efficiently, static interference should be detected so that occupied frequencies are avoided. With this increasing number of communications devices and interference sources, it is desirable for communications devices to somehow analyze channel parameters before communications are actually initiated. Such an analysis would indicate the presence of other devices and potential interference sources at certain frequencies. Once indicated, use of these frequencies could be avoided.
In Bluetooth, various proposals exist which relate to adaptive frequency hopping in which the device first analyses the whole frequency band to detect “free” channels and adapts its frequency hopping scheme correspondingly. However, existing and proposed methods such as these are time consuming because a large number of measurements are required to locate bandwidths that exhibit interference.
Moreover, the channel measuring capabilities of current WLAN and WPAN radios are limited because their channel measurements fail to cover the entire band at once. Hence, they are both power and time consuming. This drawback can be attributed in part to the sampling rates employed by the existing systems. These sampling rates are much lower than the total bandwidth in which the device can place a transmission (e.g., the entire ISM band).
For example, Bluetooth employs a sampling rate of approximately 10 mega samples per second (Msps), which is a few times greater than its symbol rate. With this kind of sampling rate, it is not possible to measure at once the entire ISM band in which Bluetooth may operate. Instead, several measurements have to be made. Not only does this technique consume considerable time and power, this technique is also very unreliable because interference could disappear (or suddenly appear) while the Bluetooth device is measuring another part of the band.
Products and devices having the capability to engage in ultra wideband (UWB) communication will exist in the near future. Such devices having both a UWB transceiver and other short-range transceiver (e.g., WLAN, WPAN, and/or Bluetooth) are referred to herein as multi-radio devices.
In connection with the emergence of UWB communications, a high rate physical layer (PHY) standard is currently being selected for IEEE 802.15.3a. There are two PHY proposals remaining in the selection process. One of these candidates is based on a frequency hopping application of orthogonal frequency division multiplexing (OFDM). The other candidate is based on M-ary Binary offset Keying. The OFDM proposal is called Multiband OFDM (MBO).
Neither of these proposals has been able to reach the required percentage of votes for acceptance. Therefore, development of these proposals are occurring simultaneously. In order to develop the OFDM proposal so that it has a larger industrial support, a new alliance called MultiBand OFDM Alliance (MBOA) was formed in June 2003.
The MBOA proposal utilizes OFDM modulation that is capable of handling communications and spectral energy measurements for channels having bandwidths (i.e., greater than 500 MHz) that are greater than many unlicensed frequency bands, such as the ISM band. These measurement capabilities arise from a high sampling rate and OFDM's utilization of fast Fourier transforms (FFTs).
Thus, devices operating according to the MBOA proposal may use their base band to measure frequency bands (such as the ISM band) because they are much narrower than 500 MHz. Accordingly, techniques are needed to employ such capabilities for the detection of interference.